1. Field of the Invention
The present invention relates to an alternating current generator for a car. More particularly, it relates to an improvement in the structure of a partition plate for a cooling fan.
2. Description of the Prior Art
Generally, in an open type a.c. generator for a car, there has been known to use a cooling fan to cool the generator, the cooling fan being generally of a centrifugal type. In the centrifugal type fan, there has been proposed to use either a Sirocco fan in which a side plate is attached to a blade itself or a partition plate in a hollow disc form is used so as to keep a predetermined distance to the blade, in order to increase efficiency of the fan. However, the fans above-mentioned have drawback of complicated structure. The structure of a conventional fan will be described in more detail.
FIG. 1 is a cross sectional view of a conventional a.c. generator for a car in which the reference numeral 1 designates a field coil; 2 and 3 respectively designate front and rear magnetic poles; 4 and 5 respectively designate front and rear blades; 6 designates a rectifier; 7 designates a brush holder; 8 designates the side plate of the rear blade 5; 9 designates a rear bracket and 10 designates a front bracket.
When the generator is actuated by the engine of a car (not shown), the blades 4 and 5 are driven and air in the vicinity of the blades 4, 5 undergoes centrifugal force to go toward the outer circumference with the result that there takes place air flow as indicated by the arrow marks a and b.
As apparent from FIG. 1 that for the front blade 4, it is easy to keep a constant distance between the front bracket 10 and the blade 4 around the entire circumference, while for the rear bracket 9, it is impossible to keep relationship as above-mentioned because of presence of the rectifier 6 and the brush holder 7. It was, therefore, necessary to place a side plate 8 facing the blade 5 to form a constant distance. As one of technique to constitute such side plate 8, there is a proposal to form it by resin-molding as shown in FIG. 2. The side plate 8 formed by resin-molding, however, has a disadvantage that it may be broken when rotated at a high speed. FIG. 3 shows a side plate formed of a metal plate. The side plate requires complicated steps of forming fitting parts in a main body, and caulking or brazing the fitting parts.
FIG. 4 shows another examples of the conventional a.c. generator in which the reference numeral 11 designates a partition plate in a hollow disc form in a portion opposing the rear blade 5 so as to provide an equivalent structure to a Sirocco fan. Provision of the partition plate 11 has disadvantages such that a number of fastening parts has to be provided in it to obtain flatness of the surface of the partition plate and that when the partition plate is to be formed by resin-molding, a molding machine having a large capacity is required because the partition plate has a large surface area.